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Swine influenza (H1N1) virus particles (virions) determined to be the cause of the April 2009 outbreak (originated in Mexico City, Mexico), coloured transmission electron micrograph (TEM). H1N1 swine flu virus (Family Orthomyxoviridae) is a strain of influenza type A that contains genetic material from bird and human influenza viruses. It is thus able to spread from human to human and cause an influenza pandemic. Symptoms are similar to those of human flu and include fever, cough, sore throat, body aches, headache, chills and fatigue. It can lead to death. Swine flu in pigs is a respiratory disease of pigs caused by a type A influenza virus. Magnification: x29,800 when shortest axis printed at 25 millimetres. Original image courtesy of the CDC.